We have cloned the ING family genes (p33ING2, p47ING3, p29ING4, and p29ING5). ING family genes have a PHD-finger motif, which is a C4HC3 zinc-finger-like motif found in nuclear proteins thought to be involved in chromatin-mediated transcriptional regulation. The function of this domain in not yet known, but in analogy with the LIM domain, it could be involved in protein-protein interaction and necessary for the assembly or activity of multicomponent complexes involved in transcriptional activation or repression. The p33ING1 protein is a regulator of cell cycle, senescence, and apoptosis. Three alternatively spliced transcripts of p33ING1 encode p47ING1a, p33ING2/ING1L. Unlike p33ING1b, p33ING2 is induced by the DNA-damaging agents etoposide and neocarzinostatin. p33ING1b and p22ING2 negatively regulate cell growth and survival in a p53-dependent manner through induction of G1-phase cell-cycle arrest and apoptosis. p33ING2 strongly enhances the transcriptional-transactivation activity of p53. Furthermore, p33ING2 expression increases the acetylation of p53 at Lys-382. Taken together, p33ING2 is a DNA damage-inducible gene that negatively regulates cell proliferation through activation of p53 by enhancing its acetylation.